714 :n'atueal history of aquatic animals. 



ance of the reproductive organ is the same in both sexes. There is no characteristic by which a 

 male Oyster can be distinguished from a female, without microscopic examination. As the repro- 

 ductive organ has an opening on each side of the body, it is usually spoken of as double, bnt in 

 the adult Oyster it forms one continuous mass, with no trace of a division into halves, and extends 

 entirely across the body and [against] the bends and folds of the digestive tract." ^ 



(The last of the foregoing statements as to the impossibility of discriminating the sexes with- 

 out the aid of the microscope is no longer true, though it was true at the time the above was 

 written. The method of discriminating the sexes discovered by the writer is discussed in another 

 portion of this sketch of the history of the Oyster.) 



The stomach is pretty definitely marked off from the other portions of the digestive tract. It 

 may be said to be that portion of the latter which is surrounded by the liver. The portion of the 

 intestine immediately following the short widened region which we regarded as the stomach is the 

 most spacious portion of the gut, and in it is lodged a very singular organ which has been called 

 the "crystalline style." This is an opalescent rod of a glass-like transparency and gelatinous 

 consistence which measures, according to the size of the Oyster, from half an inch up to one and 

 a half inches in length. Its anterior end is the largest, and in a large specimen measures nearly 

 an eighth of an inch in diameter, but at its posterior end is scarcely half as thick; both ends are 

 bluntly rounded. I fell into an error in supposing that this style was lodged in a special pouch 

 or sac as described in my report to the Maryland commissioner in 1880. The "crystalline style" 

 really lies in the first portion of the intestine and extends from the pyloric end of the stomach to 

 the first bend of the intestine, where there is a marked constriction of the alimentary canal. It 

 appears therefore to be a sort of loose valve in the cavity of the gut; its function may be to 

 prevent coarse particles of food from passing, or it may in some way assist digestion. In speci- 

 mens hardened in acid or alcohol this rod is destroyed, or at least disappears, so that I have been 

 unable to find it. The greater portion of its substance is apparently made up of water. 



The peculiar double induplication of the wall of the intestine is described in another place. 

 The faecal matters are extru ded in the form of a demi-cylinder, with one side excavated in a groove- 

 like manner. This shape of the faecal matters is due to the presence of the double fold. The faeces 

 themselves are compo sed of extremely fine particles of quartz or sand grains, the tests of diatoms, 

 organic matters, humus, cellulose, fragments of the chitinous coverings of some of the minute 

 worms and articulates, etc., which have been swallowed and digested by the animal. The anus 

 is situated on the dorsal side of the great adductor muscle where the intestine ends. 



The organs of sensation of the Oyster, though not very highly developed, are of sufficient 

 importance to merit attention. The auditory sense, although I have never been able to dissect out 

 the auditory vesicles, I am satisfied exists, because one cannot noisily approach an Oyster bank 

 where the Oysters are feeding without their hearing so that instantly every shell is closed. The 

 tentacles of the mantle are often extended until their tips reach beyond the edges of the valves. 

 If the animal in this condition is exposed to a strong light the shadow of the hand passing over it 

 is a sufficient stimulus to cause it to retract the mantle and tentacles and to close its parted valves. 

 The mantle incloses, like a curtain, the internal organs of the creature on either side, and lies next 

 the shell, and, as already stated, secretes and deposits the layers of calcic carbonate composing 

 the latter. The free edges of the mantle, which are purplish, are garnished with small, highly 

 sensitive tentacles of the same color. These tentacles are ciliated and serve as organs of touch, 

 and also appear to be to some extent sensitive to light. 



1 W. K. Brooks: Op. ci«., pp. 8-10. 



